Hybrid vehicle controller

ABSTRACT

The controller includes motor control means for controlling the drive RPM of a motor generator to reach a specified RPM less than the idle RPM when the braking condition of a foot brake is detected by a brake-operating-state detecting means while a motor generator is being rotated at an idle RPM or more. This reduces uncomfortable shock which tends to occur because of a change in the rotation of the motor during braking as much as possible to improve drive feeling.

This application is the U.S. National Stage of PCT/JP2003/010107 filedAug. 8, 2003 which claims priority from JP2002-234007 filed Aug. 9,2002, the disclosures of which are incorporated herein in theirentireties by reference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hybrid vehicle controller having an idlingstop function and, more particularly, it relates to a control device fora hybrid vehicle capable of avoiding a shock which tends to occurbetween braking and starting during motor single running.

2. Description of Related Art

For hybrid cars including an internal combustion engine (hereinafter,referred to as an engine) and a motor generator (hereinafter, referredto as a motor) as the primary drive, particularly, hybrid cars having aso-called idling stop function of stopping an engine and a motor everytime an accelerator pedal is released and a brake pedal (service brake(foot brake)) is depressed to stop the car, driving units have beenproposed that operate only the motor at startup after the stop andignite, or start, the engine, which is rotated by the motor at the pointin time when the engine rotation reaches a certain speed as described,for example, in JP-A-2001-163071.

With the hybrid-car driving unit, when the brake pedal is releasedduring stopping in which the idling stop function is activated, themotor which has been stopped until then starts to rotate at idle speedto start so-called creeping and when the brake pedal is depressed again,the motor stops. Accordingly, low-speed running can be performed bydepressing (ON) or releasing (OFF) the brake pedal during trafficcongestion or parking. “Creep” generally means that automatic carsincluding a torque converter move slowly at an engine torque though thetorque converter when a brake pedal is released without an accelerationpedal depressed and with the gear switched to a drive (D) range or areverse (R) range. “Creep” in this description, however, means that carsmove slowly not at a torque of the internal combustion engine but withtorque through a torque converter when a motor generator operates.

With the above-described hybrid-car driving units, when the motorgenerator repeats the stop and the rotation by repeating the depressionand release of the brake pedal (ON and OFF of the brake), uncomfortableshock occurs and is applied to a driver each time.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a controldevice for a hybridvehicle in which the above problems are solved byproperly controlling the motor speed when cars are braked duringcreeping by rotating only a motor after stopping with an idling stopfunction, thereby avoiding the uncomfortable shock, which could easilyoccur, as soon as possible.

A control device for a hybrid vehicle includes a motor having a rotorand a starter (i.e., torque converter) capable of transmitting thedriving forces of an engine and the motor to downstream powertransmission components and also of rotating the rotor when the drivingwheelsare braked. The control device for a hybridvehicle includesbrake-operating-state detecting means for detecting the operating stateof a brake for braking or releasing the driving wheel; and motor controlmeans capable of controlling the drive rotational speed of the motor toa predetermined rotational speed less than the idling rotational speedwhen the brake-operating-state detecting means detects the braking statewhile the motor is being rotated at an idling rotational speed or morewith the engine ignition off. Throughout this application “rotationalspeed” means a measure of rotation, for example, “revolutions per minute(RPM)”.

In the invention, “motor” means not only a so-called motor that convertselectrical energy to revolutions in a narrow sense but also a so-calledgenerator that converts revolutions to electrical energy. “Engine” meansan internal combustion engine that burns fuel to convert energy torevolutions and includes a gasoline engine, a diesel engine or the like.

Accordingly, when the braking state is detected while the motor is beingrotated at an idling rotational speed or more, the motor control meanscontrols the motor rotational speed to a predetermined rotational speedless than the idling rotational speed, eliminating a shock at the timeof switching from static friction of the motor to dynamic friction whichtends to generate every time the brake is released or applied duringcreeping, thus improving drive feeling. Driving at a rotational speedlower than the idling rotational speed at the time of braking leads toefficient reduction in power consumption.

By setting the predetermined rotational speed depending on the controlinput of the brake an optimum motor rotational speed corresponding tothe braking input control can be obtained.

Further, because the rotor is directly connected to an output shaft ofthe engine, the engine output shaft can be rotated stably by therotation of the motor to start the engine, thereby reducing, as much aspossible, the vibrations of the engine and its mount which tend togenerate at the time of engine startup.

The engine resonance rotational speed means a rotational speed in therange of large vibration at the point in time when the natural frequencyof the engine has become equal to that of the motor. The resonancerotational speed differs depending on the kind (type) of the engine,approximately from 400 to 500 rotational speed.

Because the predetermined rotational speed is less than the idlingrotational speed and larger than the engine resonance rotational speed,uncomfortable shock that tends to easily occur at the time of start andstop during creep running can be reduced as much as possible bycontrolling the motor rotational speed not to pass through the range ofthe engine resonance rotational speed every time the motor rotationalspeed decreases, thus improving drive feeling.

The motor control means stops the motor rotating at the predeterminedrotational speed at the point in time when a predetermined time haselapsed from the start of the braking. Because the motor rotating at apredetermined rotational speed is stopped at the point in time when thetime from the start of braking has elapsed, i.e., exceeds apredetermined time, it can be determined from the braking elapsed timethat a driver desires to stop the car not intermittently but completelypreventing creeping, and the motor can be stopped on the basis of thedetermination. Thus, unnecessary rotation of the motor can be preventedand power consumption can be reduced.

The control device includes control-input determination means fordetermining the braking control input of the brake. When the brakingstate of the brake is detected by a brake-operating-state detectingmeans, and the braking control input determined by the control-inputdetermination means is less than a predetermined value, the motorcontrol means does not perform switching to the predetermined rotationalspeed to maintain the idling rotational speed.

Accordingly, when the brake control input determined by thecontrol-input determination means is less than a predetermined value atthe time of detection of the braking state by the brake-operating-statedetecting means, the motor control means can control the motor not toswitch to the predetermined rotational speed to maintain the idlingrotational speed. Therefore, for example, when the braking control inputis less than 50 percent, the idling rotational speed can be maintainedwhile regarding it as a state in which creeping by the motor is desired;on the other hand, when the depression amount exceeds 50 percent, therotational speed can be switched to the predetermined rotational speedwhile regarding it as a state in which a temporary stop is desired. Inthis way, accurate motor drive control can be performed whiledetermining the driver's intention depending on the difference in brakedepression amount.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the drawings, inwhich:

FIG. 1 is a block diagram of a control device for a hybrid vehicleaccording to a first example;

FIG. 2 is a schematic block diagram of a hybrid-vehicle driving systemthat can be controlled by the control device of FIG. 1;

FIG. 3 is a partial sectional view of a specific example of the drivingsystem of FIG. 2;

FIG. 4 is a flowchart of a main routine for the drive control accordingto the first example;

FIG. 5 is a flowchart of a subroutine for the motor drive control foundas step S2 of FIG. 4;

FIG. 6 is a timing chart for the operation timing of braking operationand a motor rotational speed;

FIG. 7 is a timing chart for the operation timing of braking operationand a motor rotational speed;

FIG. 8 is a block diagram of a control device for a hybrid-vehicleaccording to a second example;

FIG. 9 is a flowchart of another subroutine for the motor drive controlfound as step S2 of FIG. 4; and

FIG. 10 is a timing chart for the operation timing of conventionalbraking operation and motor rotational speed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A first example will now be described.

Referring to FIG. 2, the primary drive of the hybrid car includes aninternal combustion engine (hereinafter, referred to as an engine) 1 anda motor generator (hereinafter, referred to as a motor) 6. Their drivingforces are outputted to an automatic transmission 8. The automatictransmission 8 includes a torque converter (starting unit) 14 thattransmits the driving forces of the engine 1 and the motor 6 todownstream power transmission components and allows rotation of a rotor13 of the motor 6 when the driving wheels are braked and an automatictransmission mechanism (multistep transmission mechanism) 16. Theautomatic transmission mechanism 16 varies the inputted driving forcedepending on a predetermined car driving condition and outputs it to thedriving wheels. The automatic transmission mechanism 16 includes aplurality of frictional engaging elements (not shown) for gear changeand a hydraulic controller (not shown) for controlling the torqueconverter 14, which provides timely gear change by varying the engagingcondition of the frictional engaging elements with a hydraulic control.

Referring now to FIG. 3, an example of the driving system of FIG. 2 willbe described. The driving system has the motor generator (hereinafter“motor”) 6 attached to the torque converter of an automatic transmission(A/T), including the engine 1 (refer to FIG. 2). The motor 6 is abrushless DC motor accommodated in a motor housing 4, and the automatictransmission 8 receives the driving forces from the engine 1 and themotor 6. The motor 6 includes a stator 12 and a rotor 13. The rotor 13is connected directly to a crankshaft (output shaft) 3 of the engine 1,as will be described later. Therefore, the motor 6 is driven to rotatewith the crankshaft 3 when the engine is running and, when the engine 1is OFF (not running), the motor 6 rotates the engine 1 through rotatingthe crankshaft 3.

The crankshaft 3 extends from the engine 1 to the automatic transmission8. A flexible drive plate 7 is fixed to the end of the crankshaft 3 witha bolt 9. A flexible input plate 10 is disposed in the position facingthe drive plate 7 with the respective ends fixed and joined togetherwith a bolt 11. The plates 7, 10 comprise a flex plate. The crankshaft 3of the engine 1 has a later-described hole 3 a in the end face thereof.

The rotor 13 of the motor 6 is formed of a large number of laminationplates in which permanent magnets are embedded and a support plate 15for fixing or supporting the lamination plates. The support plate 15includes a cylindrical hub 15 a disposed in the center of rotation, acircular disk 15 b connected to the hub 15 a and arranged along thedrive plate 7, and a cylindrical retaining section 15 c connected to theouter periphery of the circular disk 15 b. The retaining section 15 cretains the lamination plates arranged in the axial direction.

A part of the input plate 10 passes by the stator 12 of the motor 6 toextend to the outer periphery. An end 10 a of the plate extension is cutout in comb shape. A sensor 17 is disposed in the position of the motorhousing 4 facing the plate cutout 10 a. The phase of the rotor 13 of themotor 6 is detected by detecting the extension of the plate by thesensor 17. The sensor 17 is arranged at the end (adjacent to the engine)of the motor housing 4 such that it faces the outer periphery, thedetecting section of which is arranged in a recess formed in theouter-periphery extension of the motor housing 4. The sensor 17 detectsthe accurate rotational position of the rotor 13 to control the timingof a current applied to the stator 12.

On the other hand, the automatic transmission mechanism 16 of theautomatic transmission 8 is housed in a mission case and a rear case(not shown), respectively. The torque converter 14 of the automatictransmission 8 is housed in a converter housing 26. The torque converter14 includes a lockup clutch 27, a turbine runner 29, a pump impeller 30,a stator 31, and a front cover 32. The cover 32 has a center piece 33 onthe outside thereof fixed to the center of rotation.

The front cover 32 is formed of a circular-disk-shaped inner circlesurface 32 a arranged along the circular disk 15 b of the rotor 13, acylindrical middle section 32 b connected to the outer periphery of theinner circle surface 32 a along the retaining section 15 c, and an outercircle surface 32 c connected to the middle section 32 b along the outershape of the turbine runner 29 and fixed to the pump impeller 30. Thestator 12 and the rotor 13 are arranged in the substantially axialdirection on the outer periphery at the middle section 32 b of the frontcover 32. The rotor support plate 15 is supported in the center betweenthe inner surface of the retaining section 15 c of the rotor supportplate 15 and the outer surface of the front-cover middle section 32 bwith a predetermined clearance D therebetween.

The lockup clutch 27 is housed in the inner circle surface of the middlesection 32 b of the front cover 32. A spline 35 extending in the axialdirection is integrated with the inner surface of the front-cover middlesection 32 b. A plurality of outer friction plates 37 is in engagementwith the spline 35. A snap ring 39 prevents the outer friction plates 37from falling off. A piston plate 40 is movably arranged in an oil-tightmanner between the inner surface of the middle section 32 b and theouter surface of a lockup piston hub 33 a integrated with the centerpiece 33. A hub 41 connected to the turbine runner 29 is joined with aspline to an input shaft 21 in the vicinity of the lockup piston hub 33a, to which two disks 42 are fixed. The lockup clutch 27 is small indiameter so that it can be housed inside the motor 6. The lockup clutch27 is a multiplate clutch, which can surely transmit the diving forcesof the motor 6 and the engine 1 to the input shaft 21 even when both ofthe motor 6 and the engine 1 are driven.

The disks 42 support a clutch hub 43. Between the disks 42 and theclutch hub 43, a damper spring 45 is interposed to absorb impactrotation. The clutch hub 43 extends toward the outer circle surface andis bent in the axial direction. A plurality of inner friction plates 46is connected to a spline formed at the bent portion. Briefly, the outerfriction plates 37 and the inner friction plates 46 form the multiplateclutch for the lockup clutch. A predetermined oil pressure is applied toor released from an oil chamber formed between the piston plate 40 andthe front-cover inner circle surface 32 a, so that the piston plate 40is moved to control the pressure of the plate 40 applied to the outerfriction plates 37 so that the connection, release, or slip of thefriction plates 37, 46 is controlled.

An oil pump 50 is disposed between the torque converter 14 and theautomatic transmission mechanism 16. The converter housing 26 and amission case 19 are joined together with a large number of bolts 51. Apump case 52 is integrated with the mission case 19 with a large numberof bolts 53. A pump cover 55 is joined to the pump case 52 with a bolt56. The pump case 52 is positioned such that its outer peripheralsurface 52 c is fitted to the inner surface 26 a of the converterhousing 26 in oil-tight manner via an O-ring 54. A rear cover 57 weldedto the front cover 32 is integrated with the outer shell of the pumpimpeller 30. A sleeve-like impeller hub 59 is integrated with the innercircle surface of the rear cover by welding. The impeller hub 59 isrotatably supported, with a bushing 60, on the inner peripheral surfaceof the cylinder 52 a of the pump case 52 integrated with the cases 26,19. The impeller hub 59 is joined to a rotor 50 a of the oil pump 50 atthe end. In other words, the rear of the torque converter 14 isrotatably supported to the pump case 52 integrated with the converterhousing 26 via the bushing 60.

The stator 31 is connected to a one-way clutch 61. An inner race 61 a ofthe one-way clutch 61 is spline-connected to a sleeve shaft 62. The endof the sleeve shaft 62 is fixed to the pump cover 55 with a spline. Anoil seal 63 is placed between the impeller hub 59 and the pump case 52.The input shaft 21 is indirectly supported to the integrated pump case52 and pump cover 55 via the sleeve shaft 62, with a bushing or a needle65 interposed between the sleeve shaft 62 and the input shaft 21, in theinner circumferential surface of the oil pump 50.

The end of the input shaft 21 is fitted in a hole 33 b of the centerpiece 33 of the torque converter 14 such that it is in contact with anO-ring. Accordingly, the center piece 33 is supported between the inputshaft 21 and the crankshaft 3 such that the rear hole 33 b is fitted onthe input shaft 21 and the front is fitted in the hole 3 a of thecrankshaft 3. Briefly, the front of the torque converter 14 is supportedby the crankshaft 3 through the center piece 33. The crankshaft 3 isrotatably supported to an engine body (not shown) though a bearing madeof metal or the like.

The center piece 33 increases in diameter in the center of theprojection thereof. The hub 15 a of the rotor support plate 15 is incontact with the increased diameter portion 33 c to support the supportplate 15. The end of the projection of the center piece 33 alsoincreases in diameter. The increased diameter portion 33 d is in contactwith the hole 3 a of the crankshaft 3 to support the center piece 33.Specifically, the rotor support plate 15 is approximately flat shapedand is supported in the central position at a small-diameter portionextending in the direction of the inner circle surface of the rotor 13such that it is not limited in inclination by the axial contact of theincreased diameter portion 33 c of the center piece 33 with the hub 15 ain a relatively small area. The center piece 33 is also centered on thecrankshaft 3 with a predetermined inclination allowed by the increaseddiameter portion 33 d.

The front cover 32 has a set block 67 in the outer circle surface of theinner circle surface 32 a. A bolt 69 is screwed in a screw hole 67 a ofthe set block 67 through a hole 15 e of the rotor support plate 15 and ahole 10 b of the input plate 10, thereby integrating the front cover 32,the rotor support plate 15, and the input plate 10. The rotor supportplate 15 and the input plate 10 are fixed together also with a bolt 70.The circular disk 15 b of the rotor support plate 15 is large inthickness at an outer circle 15 b ₁ of the portion fixed (15 e) with thebolts 69, 70, is relatively small in thickness at an inner circle 15 b ₂and has a predetermined number of perforations 15 f.

As shown in FIG. 1, the control device for a hybrid-vehicle includes anelectronic control unit (ECU) 19. The electronic control unit 19includes an engine control means 20, a motor control means 22, abrake-operating-state detecting means 23, a throttle-position detectingmeans 25, a car-speed detecting means 36, and a hydraulic control means38.

The electronic control unit 19 further has an engine-speed sensor 44 forsensing the rotational speed of the engine 1, a motor speed sensor 47for sensing the rotational speed of the motor 6, a brake sensor 48 forsensing the ON (depression) and OFF (release) of a brake by brake pedaloperation, a throttle position sensor 58 for sensing the opening of athrottle, and a car-speed sensor 64 for sensing the travel speed of acar (car speed), connected to the input side. The electronic controlunit 19 also has the engine 1, the motor generator 6, and the automatictransmission mechanism 16, connected to the output side.

The engine control means 20 performs the controls for driving the engine1, such as stop control of the engine 1 depending on the car speedsensed by the car-speed detecting means 36 on the basis of the detectionby the car-speed sensor 64 and the brake operating state sensed by thebrake-operating-state detecting means 23 on the basis of the detectionby the brake sensor 48, later-described determination of completeignition of the engine 1, and ignition control of the engine 1. In theignition control, the engine control means 20 controls the engine 1 suchthat the driving of the engine 1 is stopped by turning off an injection(fuel injector) at the point in time when the car-speed detecting means36 detects car speed 0 km/h on the basis of the determination of thecar-speed sensor 64 and after the running is started by the rotation ofonly the motor 6 and when the throttle opening exceeds a predeterminedvalue and the engine speed exceeds a predetermined value, the injectionis turned on to rotate the engine 1.

The motor control means 22 controls current supply so as to stop therotation of the motor 6 when the running car is stopped by a brakingoperation, in synchronization with the stop of the engine 1 under thecontrol of the engine control means 20 and controls the motor 6 so as tostart running again with the crankshaft of the engine 1 in unfiredcondition when the brake pedal is released from the stop state to startthe rotation of the motor 6.

The motor control means 22 controls the motor 6 such that when thebraking state is sensed by the brake-operating-state detecting means 23while the motor 6 rotates at the idling rotational speed, an idling stopsignal is outputted to the engine control means 20 to maintain theignition off state of the engine 1 and to bring the rotational speed ofthe motor 6 to a predetermined rotational speed N1 lower than the idlingrotational speed and higher than the engine resonant rotational speed.That is, the engine resonant rotational speed is lower than the idlingrotational speed. Specifically, the motor control means 22 sets amotor-generator(MG)-rotational speed instruction value to bring themotor rotational speed to the predetermined rotational speed N1 lowerthan the idling rotational speed and higher than the engine resonantrotational speed from 400 to 500 rotational speed so that an electriccurrent corresponding to the instruction value is applied to the motor6. The predetermined rotational speed N1 may be set at, for example, 600rotational speed.

The motor control means 22 controls the motor 6 which is rotating at thepredetermined rotational speed N1 to stop at the point in time when thebraking by the brake pedal depression has elapsed for a predeterminedtime (later-described T1).

The brake-operating-state detecting means 23 senses the operating stateof a foot brake (service brake) that brakes or releases driving wheels(not shown) by brake-pedal depression on the basis of the determinationinputted from the brake sensor 48.

The throttle-position detecting means 25 detects the throttle opening byacceleration-pedal depression on the basis of the determination of thethrottle position sensor 58. The car-speed detecting means 36 determinesthe car running speed on the basis of the determination inputted fromthe car-speed sensor 64. The hydraulic control means 38 controls theoperation of a hydraulic control valve for a hydraulic servo (not shown)and so on which varies the engaging state of the plurality of frictionengaging elements of the automatic transmission mechanism 16, such as abrake and a clutch.

Referring now to the flowcharts of FIGS. 4 and 5 and the timing chartsof FIGS. 6 and 7, showing the operation timings of braking operation andmotor rotational speed, the drive control by the controller of thisembodiment will be described.

In a state in which a car having the controller is in a stopped state,when an ignition switch (not shown) is turned on and an accelerationpedal is depressed (at the time of low throttle opening), an electriccurrent is applied from a battery (not shown) to the motor generator 6,and so the motor generator 6 works as motor. Specifically, the motorcontrol means 22 of the electronic control unit 19 feeds a currentthrough a coil of the stator 12 at a proper timing to rotate the rotor13 forward at high efficiency and a first counter 66 starts to count thesingle running time of the motor 6. Thus, the rotating force isincreased at a predetermined torque ratio through the torque converter14 and transmitted to the input shaft 21.

At the startup, the injection (fuel injector) of the engine 1 does notoperate and so the engine 1 is in a stopped state, so that the carstarts only with the driving force of the motor 6. At that time, thesupport plate 15 (refer to FIG. 3) is rotated by the rotation of themotor 6, so that the crankshaft 3 is rotated through the input plate 10and so on to move the piston of the engine 1 in ignition OFF state toand fro while repeating the compression and releasing of the air in thecylinder chamber. The motor 6 has a driving characteristic that outputsa high torque during low rotational speed. In combination with anincrease in the torque ratio of the torque converter 14 with a hightorque ratio due to the first speed of the automatic transmissionmechanism 16, a car starts and runs smoothly at a predetermined torque.

In a state in which a car is running at a steady high speed, the motor 6is driven at no load to run at idle such that motor output is controlledso as to offset the torque generated by a generated back electromotiveforce. Accordingly, the car runs by the driving force of only the engine1. When the state of charge (SOC) of a battery (not shown) is low, themotor generator 6 is used as generator to regenerate the energy.

In a state in which a car stops at a light or for parking, the rotationof the motor 6 is stopped and also the engine 1 is stopped by theinjection OFF into an idling stop state without the conventional engineidling.

When the car starts from the stopped state, various conditions aredetermined in step S1 of FIG. 4. The conditions are the ON/OFF state ofthe throttle, the ON/OFF state of the ignition key (output/non-output ofa start (STT) signal), whether the present car speed exceeds apredetermined value 1 (the speed at which the car starts to run: 0km/h), the ON/OFF state of an idling-stop release signal, whether thebrake is applied, and the like. Step S1 is repeatedly performed untilthe conditions reach predetermined values and, when the conditions aresatisfied, the process shifts to step S2.

In step S2, a motor drive control (rotational speed control) isperformed for setting the rotational speed of the motor 6, which will bedescribed later. Then, in step S3, the first counter 66 that counts thesingle running time of the motor 6 is incremented. In step S4, engineignition conditions are determined. The conditions include the ON/OFFstate of the throttle, the ON/OFF state of the STT signal, the ON/OFFstate of the idling-stop release signal, and whether the count value ofthe first counter 66 exceeds a predetermined value 2 (the single runningtime of the motor 6: for example, 10 sec). The process from step S2 isrepeated until the conditions reach predetermined values and, when theconditions are satisfied, the process shifts to step S5.

In step S5, the first counter 66 and a second counter 68, that hascounted the brake-pedal depression time, are cleared. Even when the carspeed immediately after starting is relatively low, when theacceleration pedal is depressed to open the throttle to a predeterminedopening or more to accelerate or to go up a hill, in step S6, theinjection is turned on by the engine control means 20 to ignite theengine 1 with an ignition plug with the motor 6 acting as a startermotor

Upon ignition of the engine 1, in step S7, the deviation between theengine rotational speed determined by the engine-speed sensor 44 and themotor-rotational speed instruction value set by the motor control means22 is determined to determine whether the engine 1 has startedcompletely (i.e., the engine is firing properly). As a consequence, whenit is determined that the engine 1 has completely started and isproperly running, on the basis of the occurrence of the deviation, themotor control means 22 starts the torque control of the motor 6 in stepS8.

When the engine 1 starts to operate by the complete firing, the rotatingforce of the crankshaft 3 is transmitted to the support plate 15 throughthe drive plate 7 and so on, to which the driving forces of the engine 1and the motor generator 6, working as motor, are added, which istransmitted to the torque converter 14, allowing the car to run withhigh driving force. A hydraulic controller (not shown) is operated underthe control of the hydraulic control means 38 to upshift the automatictransmission mechanism 16, thereby allowing a desired rotational speedrotation to be transmitted to the driving wheels.

Referring to FIG. 5, the subroutine of the motor drive control(rotational speed control) shown in step S2 will be described. In stepS1, when the throttle-position detecting means 25 determines that thereis no acceleration pedal depression (throttle opening is zero percent)on the basis of the detection by the throttle position sensor 58 or thebrake-operating-state detecting means 23 detects the ON state of thefoot brake (time to in FIG. 6), the engine control means 20 and themotor control means 22 determine that so-called creeping is required bya driver.

Specifically, in step S11, it is determined whether the brake pedal hasbeen depressed (ON), wherein when it is determined that the brake is notturned on (not depressed), or the ON-mode foot brake has been turned off(break released) (time t₁ in FIG. 6), in step S13, the motor controlmeans 22 sets an MG-rotational speed instruction value for bringing themotor rotational speed to an idling rotational speed. Furthermore, themotor control means 22 controls the motor so that a currentcorresponding to the instruction value is fed to the motor 6 andthereafter, in step S14, clears the count by the second counter 68.

When it is determined in step S11 that the brake that had been turnedoff has been turned on (time t₂ of FIG. 6), it is determined in step S12whether the count value of the brake-pedal depression time by the secondcounter 68 is less than the predetermined time T1 (for example, 3 sec),wherein when it is determined to be still less than the predeterminedtime T1 (the interval between time t₂ and t₃ of FIG. 6), the motorcontrol means 22 controls the motor 6 to set the motor rotational speedto the predetermined rational speed N1 in step S15, increments thesecond counter 68 in step S17, and to supply a current corresponding tothe predetermined rational speed N1 in step S18. In this way, the motorrotational speed is reduced to the predetermined rational speed N1during the interval between the times t₂ and t₃ that requires no higherrotational speed than required to turn on the brake, so that powerconsumption can be saved. Thereafter, for example, when the foot brakeis released before the elapse of the predetermined time T1, the motorcontrol means 22 performs the processes of steps S11, S13, S14, and S18to increase the rotational speed of the motor 6 that has rotated at thepredetermined rotational speed N1 to an idling rotational speed.

When it is determined in step S12, that the count value of the secondcounter 68 has reached more than the predetermined time T1 (time t₃′ ofFIG. 7) (No), the motor control means 22 sets the rotational speed ofthe motor 6 to 0 in step S16 and controls the motor 6 to operate inaccordance with the setting (or stop the rotation) in step S18. Thus,current supply to the motor 6 is stopped and so the actual motorrotational speed (MG actual rotational speed) gradually decreases fromthe time t₃′ of FIG. 7 to the actual stop time t₄.

Another exemplary embodiment will be described with reference to thedrawings. FIG. 8 is a block diagram of a control device for ahybrid-vehicle according to this embodiment and FIG. 9 is a flowchart ofa subroutine of the embodiment for the motor drive control in step S2 ofFIG. 4. Although FIG. 8 of this embodiment is different from FIG. 1 inthat the electronic control unit 19 includes a control-inputdetermination means 18, other parts are substantially the same, andprincipal parts are given the same numerals and a description of theother components is omitted.

Referring to FIG. 8, the control-input determination means 18 determinesthe depression amount of the brake pedal (braking amount, brake stroke)in addition to the depression (ON) and the release (OFF) of the brakepedal from the detection of the brake sensor 48. The motor control means22 inputs the determination of the brake stroke by the control-inputdetermination means 18, compares the brake stroke with a predeterminedstroke A, and performs the later-described controls on the basis of thecomparison. The brake stroke is defined as a depression ratio, forexample, when a state in which the brake pedal is depressed to themaximum (full brake) is assumed to be 100 percent and a state in whichthe brake pedal is released (brake OFF) is assumed to be zero percent;thus, a 50-percent brake stroke is the middle amount between the fullbrake and the brake OFF.

Specifically, according to the motor drive control of the embodiment,first, the motor control means 22 determines in step S20 of FIG. 9whether the brake stroke has reached the predetermined stroke A or more.As a consequence, when it is less than the predetermined stroke A, instep S22, the motor control means 22 clears the count of the secondcounter 68 which has counted the depression time of the brake pedal.Furthermore, in step S23, the motor control means 22 sets the rotationalspeed of the motor 6 to a rotational speed (predetermined rotationalspeed) corresponding to the brake stroke. In other words, in this case,because the braking operation is performed so that the stroke does notexceed the predetermined stroke A, the rotational speed is set tomaintain the idling rotational speed as if the braking operation was notperformed. The motor control means 22 controls the motor 6 so that it issupplied with a current corresponding to the set rotational speed. Thesetting of the rotational speed (predetermined rotational speed) in stepS23 can be given by, for example, the expressionidling rotational speed·{(current stroke·A)×(idling rotationalspeed·N1)/(100·A)}.

On the other hand, when it is determined in step S20 that the brakestroke has reached the predetermined stroke A or more, the motor controlmeans 22 determines in step S21 whether the count of the brakedepression time by the second counter 68 is less than the predeterminedtime T1 (refer to FIGS. 6 and 7). As a consequence, when the brakedepression time does not exceed the predetermined time T1 (Yes), themotor control means 22 increments the second counter 68 in step S24 andsets a motor rotational speed corresponding to the brake stroke in stepS23. In other words, in this case, as the stroke is the predeterminedstroke A or more, the motor rotational speed is set to be decreased tothe predetermined rotational speed N1 (refer to FIGS. 6 and 7). Themotor control means 22 controls the motor 6 so that it is supplied witha current corresponding to the set motor rotational speed.

When it is determined in step S21 that the count of the brake depressiontime has reached the predetermined time T1 or more (No), the motorcontrol means 22 sets the motor rotational speed to 0 rotational speedin step S25 and controls the motor 6 to operate in correspondence withthe setting (to stop the revolution) in step S26.

As set forth hereinabove, according to the exemplary embodiments, whenthe brake-operating-state detecting means 23 has sensed the brakingcondition while the motor 6 is being operated at an idling rotationalspeed (or more than the rotational speed) with the engine 1 unfired, themotor control means 22 controls the rotational speed of the motor 6 soas to reach the predetermined rotational speed N1 less than the idlingrotational speed, so that the motor 6 can continue to rotate at thepredetermined rotational speed N1 without stop when the brake is appliedduring creeping. This eliminates the shock at the time of switching fromthe static friction of the motor 6 to dynamic friction which tends tooccur every time the brake is released or applied during creeping, thusimproving drive feeling. Driving at an rotational speed lower than theidling rotational speed during braking reduces power consumptioneffectively. Furthermore, because the rotor 13 is directly connected tothe crankshaft 3 of the engine 1, the crankshaft 3 can be stably rotatedby the rotation of the motor to start the engine, thus reducing, as muchas possible, the vibrations of the engine 1 and its mount which tend tooccur at the start of the engine.

Referring to FIG. 10, for example, with the conventional type in whichthe MG-rotational speed instruction value is set so as to stop the motorrotational speed every time the brake pedal is depressed, the rotationalspeed passes through the range of the engine resonance rotational speedevery time the rotating motor 6 decreases in rotational speed toward astop range and increases in rotational speed from the stop range to anidling rotational speed in response to the brake ON and OFF. Thus,uncomfortable shock due to the vibrations generated at the time of thepassage is applied to a driver every time together with theabove-mentioned shock due to the switching from the static friction tothe dynamic friction. According to the exemplary embodiments, however,the predetermined rotational speed N1 for the brake pedal depression isset so as to exceed the engine resonance rotational speed. Accordingly,the motor rotational speed does not pass through the range of the engineresonance rotational speed every time the motor rotational speeddecreases, so that the uncomfortable shock that tends to occur everytime the brake is released or applied can be reduced as much aspossible, thus improving drive feeling.

According to the first exemplary embodiment, the motor 6 rotating at thepredetermined rotational speed N1 is stopped at the point in time whenthe braking has elapsed the predetermined time T1. Accordingly, it canbe determined from the braking elapsed time that a driver desires tostop the car not intermittently but completely during creeping, and themotor 6 can be stopped from the determination. Thus, unnecessaryrotation of the motor 6 can be saved and so power consumption can besaved.

According to the second exemplary embodiment, in a state in which thebrake stroke (brake control input) determined by the control-inputdetermination means 18 is less than a predetermined value when thebraking state is sensed by the brake-operating-state detecting means 23,the motor control means 22 controls the motor not to switch to thepredetermined rotational speed N1 to maintain the idling rotationalspeed. Accordingly, for example, when the brake stroke is less than 50percent, the idling rotational speed can be maintained while regardingit as a state in which creeping by the motor 6 is desired; on the otherhand, when the brake stroke exceeds 50 percent, the rotational speed canbe switched to the predetermined rotational speed N1 while regarding itas a state in which temporary stop is desired. In this way, correctmotor drive control can be performed while determining the driver'sintension depending on the difference in brake stroke (brake depressionamount). Furthermore, because the motor control means 22 sets thepredetermined rotational speed N1 depending on the brake strokedetermined by the control-input determination means 18, an optimum motorrotational speed corresponding to the brake stroke can be given.

As set forth hereinabove, the control device for a hybrid-vehicle isuseful for vehicles such as passenger cars, trucks, and buses and, moreparticularly, for vehicles that require the prevention of uncomfortableshock at the time of braking during creeping produced only by motordriving.

1. A control device, for a hybrid vehicle having a motor including arotor and a starter capable of transmitting the driving forces of anengine and the motor to downstream power transmission componentscomprising: brake-operating-state detecting means for detecting theoperating state of a brake for braking or releasing the driving wheel;and motor control means capable of controlling the rotational speed ofthe motor to a predetermined rotational speed less than the idlingrotational speed when the brake-operating-state detecting means detectsthe braking state while the motor is being rotated at an idlingrotational speed or more with the engine ignition off.
 2. The controldevice for a hybrid vehicle according to claim 1, wherein the motorcontrol means sets the predetermined rotational speed depending on thecontrol input of the brake.
 3. The control device for a hybrid vehicleaccording to claim 2, wherein the rotor is directly connected to anoutput shaft of the engine.
 4. The control device for a hybrid vehicleaccording to any of claim 3, wherein the predetermined rotational speedexceeds an engine resonance rotational speed.
 5. The control device fora hybrid vehicle according to claim 4, wherein the motor control meansstops the motor rotating at the predetermined rotational speed at thepoint in time when a predetermined time has elapsed from the start ofthe braking.
 6. The control device for a hybrid vehicle according toclaim 5, comprising brake operating amount determination means fordetermining the brake operating amount of the brake, wherein when thebraking state of the brake is detected by the brake-operating-statedetecting means, when the brake operating amount determined by the brakeoperating amount determination means is less than a predetermined value,the motor control means does not perform switching to the predeterminedrotational speed to maintain the idling rotational speed.
 7. The controldevice for a hybrid vehicle according to claim 3, wherein the motorcontrol means stops the motor rotating at the predetermined rotationalspeed at the point in time when a predetermined time has elapsed fromthe start of the braking.
 8. The control device for a hybrid vehicleaccording to claim 2, wherein the predetermined rotational speed exceedsan engine resonance rotational speed.
 9. The control device for a hybridvehicle according to claim 8, wherein the motor control means stops themotor rotating at the predetermined rotational speed at the point intime when a predetermined time has elapsed from the start of thebraking.
 10. The control device for a hybrid vehicle according to claim2, wherein the motor control means stops the motor rotating at thepredetermined rotational speed at the point in time when a predeterminedtime has elapsed from the start of the braking.
 11. The control devicefor a hybrid vehicle according to claim 1, wherein the rotor is directlyconnected to an output shaft of the engine.
 12. The control device for ahybrid vehicle according to claim 11, wherein the predeterminedrotational speed exceeds an engine resonance rotational speed.
 13. Thecontrol device for a hybrid vehicle according to claim 12, wherein themotor control means stops the motor rotating at the predeterminedrotational speed at the point in time when a predetermined time haselapsed from the start of the braking.
 14. The control device for ahybrid vehicle according to claim 11, wherein the motor control meansstops the motor rotating at the predetermined rotational speed at thepoint in time when a predetermined time has elapsed from the start ofthe braking.
 15. The control device for a hybrid vehicle according toclaim 1, wherein the predetermined rotational speed exceeds an engineresonance rotational speed.
 16. The control device for a hybrid vehicleaccording to claim 15, wherein the motor control means stops the motorrotating at the predetermined rotational speed at the point in time whena predetermined time has elapsed from the start of the braking.
 17. Thecontrol device for a hybrid vehicle according to claim 1, wherein themotor control means stops the motor rotating at the predeterminedrotational speed at the point in time when a predetermined time haselapsed from the start of the braking.
 18. The control device for ahybrid vehicle according to claim 1, comprising brake operating amountdetermination means for determining the brake operating amount of thebrake, wherein when the braking state of the brake is detected by thebrake-operating-state detecting means, when the brake operating amountdetermined by the brake operating amount determination means is lessthan a predetermined value, the motor control means does not performswitching to the predetermined rotational speed to maintain the idlingrotational speed.
 19. A control device, for a hybrid vehicle having amotor including a rotor and a starter capable of transmitting thedriving forces of an engine and the motor to the downstream of powertransmission and rotating the rotor with a driving wheel in thedownstream of power transmission braked, comprising: abrake-operating-state detector that detects the operating state of abrake for braking or releasing the driving wheel; and a motor controllercapable of controlling the rotational speed of the motor to apredetermined rotational speed less than the idling rotational speedwhen the brake-operating-state detecting means detects the braking statewhile the motor is being rotated at an idling rotational speed or morewith the engine ignition off.
 20. A method for controlling a hybridvehicle having a motor including a rotor and a starter capable oftransmitting the driving forces of an engine and the motor to thedownstream of power transmission and rotating the rotor with a drivingwheel in the downstream of power transmission braked, comprising:detecting the operating state of a brake for braking or releasing thedriving wheel; and controlling the rotational speed of the motor to apredetermined rotational speed less than the idling rotational speedwhen the brake-operating-state detecting means detects the braking statewhile the motor is being rotated at an idling rotational speed or morewith the engine ignition off.